A liquid discharge recording head is mounted in a liquid discharge recording apparatus that performs recording by discharging a liquid such as ink. The available kinds of liquid discharge recording heads include a liquid discharge recording head that uses an electricity-heat transducing element as a recording element that generates energy that discharges a liquid. When an electric control signal for recording is sent to the electricity-heat transducing element, electrical energy is converted into heat energy to generate heat. The electricity-heat transducing element is disposed in the vicinity of a discharge port of the liquid discharge recording head. The discharge port is an opening that discharges a liquid. A liquid in the vicinity of the electricity-heat transducing element is instantaneously heated by the heat energy that is generated by the electricity-heat transducing element. At this time, as the result of bubble pressure that is generated by boiling of the liquid, a liquid in the vicinity of the discharge port is discharged from the discharge port. Thus, the liquid discharge recording apparatus causes liquid to adhere to a recording medium that is arranged facing the discharge port to thereby perform recording on the recording medium.
One example of the above described liquid discharge recording head is disclosed in Japanese Patent No. 3,592,208. FIG. 9 is a perspective view of a recording element unit included in a liquid discharge recording head described in Japanese Patent No. 3,592,208. FIG. 10 is a sectional view of the recording element unit along a line X-X in FIG. 9. FIG. 11 is a sectional view of the recording element unit along a line XI-XI in FIG. 9.
The recording element unit includes a recording element substrate 1 that has a discharge energy generating element (recording element) 4 that generates energy that discharges a liquid, and a flexible wiring board 11. The recording element substrate 1 is fixedly supported by a supporting member 8, and is provided with discharge ports 6 that discharge a liquid. The flexible wiring board 11 is mounted to the supporting member 8 via a supporting board 9.
The flexible wiring board 11 and the supporting board 9 have an opening part. The recording element substrate 1 is integrated into the opening part. An electrode 7 is formed in the recording element substrate 1. A stud bump 14 is provided on the electrode 7. An electrode lead 13 that is electrically connected to the electrode 7 of the recording element substrate 1 is provided in the flexible wiring board 11. A recess 17 is formed between the recording element substrate 1 and the flexible wiring board 11 and supporting board 9. A first sealing resin 18 that has elasticity after curing is filled in the recess 17. Electrically connecting parts between the recording element substrate 1 and the flexible wiring board 11 (that is, the electrode 7, the stud bump 14, and the electrode lead 13) are covered by the first and second sealing resins 18 and 19. It is thereby possible to prevent an electrical connection fault that occurs due to one of the electrically connecting parts, for example, coming into contact with a liquid such as ink or being subjected to an external impact. Since the first sealing resin 18 has elasticity after curing, cracks in the recording element substrate 1 at the time of curing are suppressed and the electrically connecting parts are also protected from an external force.
Recently, full-line type recording heads in which a plurality of recording element substrates are arranged on a supporting member are also being constructed to execute high-speed recording. According to one example of a full-line type liquid discharge recording head, recording element substrates are aligned in two rows along a direction in which discharge ports formed in the recording element substrates are aligned. By lengthening the liquid discharge recording head in this manner, it is possible to support recording onto a large-sized recording medium.
A recording element substrate in which discharge ports are formed must be mounted with precision on a supporting member. Particularly in the case of a liquid discharge recording head that includes recording element substrates that have a long shape, it is necessary to mount the recording element substrates with a high level of accuracy, and if the mounting positions are misaligned, stripes or unevenness arise in an image that is recorded by the discharged liquid.
According to Japanese Patent No. 3,592,208, electrically connecting parts between the recording element substrate 1 and the flexible wiring board 11 are sealed with the first sealing resin 18 that has elasticity after curing and the second sealing resin 19 that has an extremely high degree of hardness after curing. However, referring to FIG. 10, it can be seen that one part of the first sealing resin 18 is exposed at the surface. There is thus the problem that if the first sealing resin 18 has a low modulus of elasticity, the first sealing resin 18 weakens with respect to an external force and the durability of the liquid discharge recording head decreases.
Further, there is a tendency for the adhesiveness between two kinds of sealing resins that have a different modulus of elasticity or linear expansivity to each other to be weak. This is because when two kinds of sealing resins have a different modulus of elasticity or linear expansivity to each other, the sealing resins are affected by each other's force when a temperature change occurs. Accordingly, if the adhesion between the first sealing resin 18 and the second sealing resin 19 decreases, there is the risk that liquid will enter at the boundary surface between the sealing resins 18 and 19, and the liquid will reach an electrically connecting part. Consequently, the durability of the liquid discharge recording head will decrease.
The full-line type liquid discharge recording head is often used for business purposes or industrial purposes, and the cost of the liquid discharge recording head is high. Therefore, since it is important for a full-line type liquid discharge head to have a high level of durability, it is desirable to solve the above problem in particular.
One method that may be considered in order to increase the adhesiveness between two kinds of sealing resins is to use two kinds of sealing resins for which the modulus of elasticity or linear expansivity are the same level. However, in the liquid discharge recording head described in Japanese Patent No. 3,592,208, when the first sealing resin 18 and the second sealing resin 19 are formed from material that have values of the same level with respect to the modulus of elasticity or linear expansivity, there is the possibility that a new problem will arise. The new problem is described below.
When the modulus of elasticity of both the first and second sealing resins 18 and 19 is low, the sealing resins 18 and 19 are weakened with respect to an external force. Therefore, if an external force is applied to the sealing resins 18 and 19 by wiping or a paper jam or the like, a failure may occur at the electrically connecting parts that are sealed by the sealing resins 18 and 19.
When the modulus of elasticity of both the first sealing resin 18 and the second sealing resin 19 is high, a different problem arises. Even when the modulus of elasticity of both the first and second sealing resins 18 and 19 is high, if there is a difference between the linear expansivity of the recording element substrate 1 and the linear expansivity of the supporting member 8, a difference arises in the deformation amount of the recording element substrate 1 and the supporting member 8. The first sealing resin 18 is adhered to the supporting member 8 and is formed around the circumference of the recording element substrate 1. Hence, when the supporting member 8 expands or contracts, the first sealing resin 18 adhered to the supporting member 8 applies a force to the recording element substrate 1. The recording element substrate 1 is warped by the force. In particular, when the supporting member 8 changes shape in the direction of contraction, the first sealing resin 18 applies a force in a direction that causes the recording element substrate 1 to contract, and as a result the recording element substrate 1 becomes warped.
A large change in temperature occurs when the sealing resins 18 and 19 are subjected to thermal curing. In particular, the first sealing resin 18 around the circumference of the recording element substrate 1 cures when the sealing resins 18 and 19 are heated. Thereafter, when the sealing resins 18 and 19 are cooled to ambient temperature, the recording element substrate 1 is warped by a force received from the sealing resin 18. In this case, the recording element substrate 1 maintains the warped state under ambient temperature. When the recording element substrate 1 warps, there is the risk that the positions of discharge ports 6 formed in the recording element substrate 1 will be misaligned and result in a decline in the printing quality.
If the recording element substrate 1 is long in the direction in which discharge ports are aligned, a difference in a deformation amount of the recording element substrate 1 and a deformation amount of the supporting member 8 increases further, and warping of the recording element substrate 1 also increases in accordance with the difference in the deformation amounts. As a result, not only does the printing quality decline, but there is also the possibility that the recording element substrate 1 will come unstuck from the supporting member 8 or that the recording element substrate 1 will break.